Levels of type 1 (insulin dependent) diabetes among Finnish children have more than doubled in the past 25 years, with the increase set to continue. A combination of genetic and lifestyle factors are the likely cause, conclude authors of an Article in this weeks Diabetes Special Issue of The Lancet.
A steady increase in the incidence of type 1 diabetes has been reported worldwide, with the trend most pronounced in children aged four years and younger. The average increase per year has been 2.5 -- 3.0% worldwide, but with a huge variation between individual countries. For example, the lowest incidence occurs in Venezuela and China, and the highest in Finland and Sardinia. The increase in incidence is believed to be because of manifestation at a younger age, rather than a worldwide increase in the lifetime number of patients with the disease. A previous report showed a steady increase in the incidence of type 1 diabetes in Finland between 1965-96; Dr Valma Harjutsalo, National Public Health Institute, Helsinki, Finland, and colleagues investigated present trends in the disease in Finland and predicted the number of children who will have it in the future.
The research team analysed three Finnish registers: the National Public Health Institute Diabetes register, the Central Drug Register and the Hospital Discharge Register, looking at the time period 1980-2005. Patients with type 2 diabetes were excluded, as were those with diabetes occurring secondary to other conditions, such as steroid use, Down's syndrome, and congenital malformations of the pancreas.
They found that 10737 children -- 5816 boys and 4921 girls -- were diagnosed with type 1 diabetes before 15 years of age during 1980-2005. Incidence more than doubled in this period, from 31.4 per 100000 in 1980 to 64.2 per 100000 in 2005. In children aged 0-4 years the increase was the largest, with an average annual increase of 4.7%. The overall boy-to-girl ratio of incidence was 1.1 to 1; at the age of 13 years, it was 1.7 to 1, and the incidence peak for girls (at 10 years) occurred three years before that for boys (at 13 years). Based on these data, the predicted cumulative number of new cases of type 1 diabetes before 15 years of age between 2006 and 2020 is around 10800. Finland had exceeded its predicted 2010 incidence level by 2000.
The onset of type 1 diabetes is attributed to both genetic risk factors and environmental triggers. High birthweight and early weight gain in infancy have been implicated as risk factors for type 1 diabetes. Levels of obesity/being overweight in Finnish children have increased in past two decades and particularly in the past 10 years — with the proportion of obese children between 5 and 15 years rising from 9.5% in the mid-1980s to 20% now. The fall in birthweight over the same period emphasises the increased weight gain after birth. The authors warn that, should levels of type I diabetes continue to increase, the number of patients with serious diabetic complications, such as diabetic nephropathy, will also rise. They conclude: "The incidence of type 1 diabetes continues to increase sharply in Finland, where it has been documented to be the highest in the world since the 1950s. Evidence does not support the theory that the increase results only from a younger age at onset of the disease. The steep increase in incidence noted in the last half of the 1990s might represent a serious signal about unhealthy changes in our everyday environment that affect the penetrance of type I diabetes susceptibility genes."
In an accompanying Comment, Dr Mark Myers, Monash University Melbourne, Australia and Professor Paul Zimmet, Monash University Melbourne and International Diabetes Institute, Melbourne, discuss the possible causative effects of exposure to various agents in the womb on type 1 diabetes. They say: "The case for an environmental contribution to the cause of type 1 diabetes is compelling. However, identification of probable agents is the ultimate challenge because they might be ubiquitous, and the hardest cause of a disease to identify is that which is universally present. There seems little doubt that we have underestimated the complexity of this form of diabetes -- new ideas are clearly needed to stop the disconcerting acceleration of incidence."
Dr Valma Harjutsalo, National Public Health Institute, Helsinki, Finland T) +358 9 4744 8632 E) valma.harjutsalo@ktl.fi
Professor Paul Zimmet, Monash University Melbourne and International Diabetes Institute, Melbourne currently in Japan T) +81-9061105521 E) pzimmet@idi.org.au
http://multimedia.thelancet.com/pdf/press/diabetes1.pdf
Journal
The Lancet